Recently in the production of semiconductor elements and liquid crystal display elements, pattern size reduction has been developed rapidly with advances in lithography techniques. Accordingly, there is a demand for high resolution such as a pattern having a width of 50 nm or less.
For pattern size reduction, in general, short wavelength exposure sources has been increasingly used. Besides the currently used KrF excimer laser, lithography techniques using exposure lights such as ArF, F2, EUV, x-rays, electron beams and other charged particle beams have been proposed.
Especially, pattern forming techniques using exposure to electron beams and EUV are positioned as the second-generation or the third-generation lithography techniques, and there is a demand for the development of a negative resist for forming the gate layer of a semiconductor integrated circuit, which meets all the requests for high sensitivity, high resolution and low line edge roughness (LER). As the resist material which meets such requests, a chemically amplified photosensitive composition is used, which utilizes the catalytic reaction of acid for the purpose of increasing sensitivity. A negative chemically amplified photosensitive composition comprises an alkali-soluble resin, an acid generator component which produces acid by exposure to light, a crosslinking agent, a basic compound, etc. When such a photosensitive composition is exposed to light, a crosslinking bond is formed between the resin and crosslinking agent by the action of acid produced from the acid generator component by the exposure; therefore, the photosensitive composition is changed from an alkali-soluble composition to an alkali-insoluble composition. Also, pattern exposure is possible with a smaller exposure amount since the acid produced by the crosslinking reaction catalytically repeats reaction. On the other hand, in the chemically amplified photosensitive composition, there is a contradictory relationship between sensitivity, resolution and LER, and an issue for the composition is how to balance them.
A resist material based on a polymer having a weight average molecular weight of about 10,000 or more has been used for semiconductor lithography.
However, such a polymer material has a large molecular weight and a wide molecular weight distribution, so that there is a limit to decreasing resolution or LER.
Accordingly, low-molecular-weight materials having a low molecular weight and a small molecular size have been under development, which are expected to have better resolution than polymer materials and smaller contribution to increasing LER, Examples of negative resists based on such low-molecular-weight materials include a resist comprising calix resorcinarene and a derivative thereof (Patent Literature 1 and Non-Patent Literature 1), a resist comprising a low-molecular-weight polyphenol compound derivative (Non-Patent Literature 2) and a resist comprising a cyclic polyphenol compound derivative (Patent Literature 2).
In Patent Literatures 1 and 2,2,6-bis(hydroxymethyl)-4-methylphenol (MBHP) is used as the crosslinking agent component, while methylolmelamine and methylated urea resin are used in Non-Patent Literatures 1 and 2, respectively. However, even in the case of using any of the above as the crosslinking agent component, demands for excellent sensitivity, resolution and resist shape under exposure to electron beams are not satisfied enough.